A press conference in support of a Boston city councilor's proposal to ban the sale of dogs, cats and rabbits from commercial breeders turned testy on Monday when a pet store owner showed up to protest.

Pet Express co-owner Robert Mellace railed against the ordinance, sponsored by City Councilor Matt O'Malley, which has been dubbed the "puppy mill bill."

Pet Express, which has storefronts in Lynn, Saugus, Braintree and Danvers, does not have a location in Boston.

He challenged O'Malley on the definition of "puppy mill."

"What's a puppy mill?" Mellace asked. "Licensed or unlicensed?"

"I don't know the answer to that," O'Malley replied.

"Then you shouldn't be the one putting this bill through," Mellace said.

In an interview, Mellace said his store vigorously researches its breeders before sourcing their animals, and said he wanted to speak up for other storeowners who do the same.

"They're trying to paint all pet stores with the same brush that no matter what you do you're buying from a puppy mill," Mellace told Metro.

Although his business wouldn't be impacted by a Boston ordinance, he said he worried about other municipalities following Boston's lead.

A separate bill to regulate animal sales statewide is pending in the Legislature. Mellace said he hoped the city would await the results of that process and not support an outright ban.

The statewide effort would set new restrictions on pet-buying, among them making it illegal to sell many pets who are younger than 8 weeks old, or to sell animals from breeders with records of federal welfare violations. It would also require storeowners to cover medical costs for sick animals customers purchase.

“The state bill is more of a restriction than a prohibition,” Kara Holmquist, the MSPCA’s director of advocacy, told Metro.

The MSPCA has endorsed the bill, and Holmquist called it “a step in the right direction.”

By the MSPCA’s count, there are 17 stores in the state currently selling pets from breeders.

In an interview, O'Malley clarified that his proposal would ban all sales of commercially bred animals in Boston stores, both from licensed and unlicensed breeders. It would remain legal for city residents to purchase pets from licensed breeders directly, he said.

He told Metro he couldn't speak to Mellace's claims about ethically sourcing animals, but stood by his position that the city needs to target pet store sales to address cases of pets raised in "abhorrent conditions." Would-be pet owners should instead look to shelters, he said.

"Puppy mills are a thriving industry because of pet stores," he said. "I hear what he's saying, but I still believe very strongly that the greater good of this bill is going to help pets and their owners."

There are no stores inside the city selling puppies, but one — The Pet Shop in Allston — sells rabbits, according to MSPCA spokesman Rob Halpin.

The Pet Shop's owner, Jim Gentile, told the Boston Globe on Sunday the proposal would deal a blow to his business.

"To me it just makes no sense to drive a business out of the city of Boston," Gentile told the paper.

O'Malley said he sponsored the ordinance to stop other pet stores from opening in the future, adding that he hoped the move in Boston would be one other cities and towns in Massachusetts would also take.

O'Malley's bill would also ban animal sales in parks and on city streets. Boston would be among more than 120 municipalities to adopt similar ordinances, according to the MSPCA.

Laura Hagen,MSPCA-Angell's deputy director of advocacy, said in a statement she also supported the measure.

“We have seen a sharp increase in the number of rabbits surrendered to our Boston adoption center — a 50 percent rise in the last year alone — due in part to continued rabbit sales in pet stores, too many of which end up homeless,” Hagen said. “We applaud this legislation and urge the city to pass it without delay.”

O'Malley filed the ordinance on Monday. He said he plans to introduce it to his colleagues on the City Council on Wednesday, then schedule a hearing on the subject at a to-be-determined date.